A carboxylic ester that is the 2-(p-hydroxyphenyl)ethyl ester of (3S)-4-formyl-3-(2-oxoethyl)hex-4-enoic acid. Oleocanthal is found in olive oil but it is not clear whether the natural product is a mixture of E/Z isomers or a single isomer as the two isomers readily interconvert in solution; most pharmacological studies will have been performed using a mixture.